Storage tube with signal multiplication adjustment



D. CHARLES March 15, 1966 STORAGE TUBE WITH SIGNAL MULTIPLICATION ADJUSTMENT Filed March 6 1965 RN 3 Q Q6 S Y 2% on .m m wn 3 A M. ID

United States Patent Office 3,240,988 Patented Mar. 15, 1966 6 Claims. (c1. s1s 12 The present invention relates to an electronic storage tube of the type having a target, a writing gun and a read-out gun, and more particularly to improvements in the target and control thereof.

Known in the prior art are the analyser storage tubes operating by utilization of the phenomena of electro bombardment induced conductivity, that is, comprising a target composed of a metallic layer and of an insulating layer of dielectric material such as zinc sulfide, which has the property of becoming momentarily conductive when fast electrons penetrate into the insulating layer. This target is bombarded on the metallic side thereof by a beam of fast electrons carrying the input signal, these electrons traversing the metallic layer and penetrating into the insulating layer which they traverse more or less completely. Along their paths within the insulating material, these fast electrons liberate a large quantity of secondary electrons which, however, cannot escape to the outside as the velocity thereof is relatively too small to permit the same to traverse a solid medium or environment. The paths of each primary electron are therefore staked out by the secondary electrons which are liberated but remain in the interior of the insulating material. The insulation becomes therefore momentarily conductive which constitutes the phenomenon of induced conductivity. On the side of the insulating face, the target is explored by a reading beam, such exploration producing an emission by the target of electrons of which the current, collected in any suitable manner, constitutes the output signal.

This output signal needs to be adjusted, and to do so it is usual to act on the coefiicient of multiplication of the target, that is on the number of secondary electrons liberated within the insulating layer by each primary electron. This coefficient depends obviously on the speed of the incident primary electron in such a manner that the most direct means of variation of this coeflicient is the action 'on the primary speed, that is on the accelerating voltage of the fast beam. Nevertheless, experiments indicate that a relatively rather large amplitude of variation of this voltage is necessary to obtain a relatively slight variation of the coefficient of multiplication, and that additionally it is difficult to command these voltage variations in a sufiiciently rapid manner to follow, for example, an electric signal.

The present invention provides another means of variation of the coeflicient of multiplication of the target which permits obtaining the desired effects without having to overcome the inconveniences mentioned hereinabove.

According to the present invention, there is placed within the analyser storage tubes of the type described a target having induced conductivity which carries on the insulating face thereof, on the side of the read-out gun, a grid carried at a potential of which the regulation acts on the coefficient of multiplication of the target.

It is already known, particularly in the so-called storage tubes having a barrier grid, to provide targets comprising a metallic layer, an insulating layer and a grid on the insulating face of this layer. Nevertheless, such prior art arrangement does not relate to targets having induced conductivity, for the insulation utilized does not have the property of conferring to the target a high coefficient of multiplication, that is, to become momentarily conductive under the penetration of fast electrons.

The present invention therefore aims at a novel target structure with induced conductivity, as well as at storagetype analyser tubes to which the same is applied.

Accordingly, it is an object of the present invention to provide an analyser storage tube of the type described hereinabove having a target with induced conductivity which eliminates, by simple means and in a highly effective manner, the drawbacks and shortcomings of the prior art mentioned hereinabove.

It is another object of the present invention to provide a storage tube structure having a target with induced conductivity of which the coefficient of multiplication may be readily adjusted and controlled by simple means that may be readily and accurately manipulated.

Still another object of the present invention resides in the provision of an adjusting arrangement for adjusting the coeflicient of multiplication of induced conductivitytype targets for storage tubes which requires only relatively low adjusting voltages, utilizes relatively simple structures and permits a wide range of variations in the coefiicient of multiplication.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention and wherein:

FIGURE 1 is a longitudinal cross sectional view through an analyser storage tube including a target with induced conductivity and provided, on the insulating face thereof, with a grid in accordance with the present invention, and in which the input signal is, for example, an electric signal sequential in time,

FIGURE 2 is a partial cross sectional view, on an enlarged scale, of the induced conductivity target in accordance with the present invention together with a schematic showing of the associated control circuits, and

FIGURE 3 is a partial plan view of the induced conductivity target in accordance with the present invention.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, and more particularly to FIGURE 1, reference numeral 1 designates therein an evacuated enclosure on the inside of which are found the usual elements of an analyser storage tube producing an electric signal in response to an electric signal applied to the input thereof. These elements comprise:

A first so-called writing gun structure including a cath ode 2, a Wehnelt electrode 3, accelerating and focusing electrodes or anodes 4, 5 and 6, and deflection plates 7 and 8 in two orthogonal planes, whereby the deflection system is assumed to be of the electrostatic type, it being, however, understood that this is only for illustrative purposes without limiting the present invention to this particular deflection system. This writing gun structure is fed or supplied by way of the pins 9, whereby the cathode 2 is carried, for example, at 8 to -10 kv. with respect to the anodes 4 and 6 which are connected to ground. This beam receives the modulation by a signal applied across the capacity 10 connected to the terminal of a resistance 11 interconnected between the pin 9 and the supply terminal 12;

A target with induced conductivity 13, of which the details according to the present invention will be described more fully hereinafter; this target comprises a metalized face turned toward the writing gun structure, and an insulating face turned in the opposite direction.

Near the insulating face of the target 13 is disposed a hollow cylinder 14 forming a collector of which the output through the passage 15 is connected, on the one hand with a resistance 16 to which is applied by the terminal 17 an adjustable bias voltage V equal to some tens of positive volts with respect to the potential of the target 13, and on the other, to a condenser 18 across which is taken off the output signal at 19.

Between the collector 14 and the target 13 is disposed, according to well-known techniques, a spot corrector ring 20 of which the output through the passage 21 receives by way of terminal 22 an adjustable voltage V,, for example, between 15 and +15 volts with respect to the voltage applied to the collector 14.

Gn the side of the insulating face of the target is disposed a reading system, composed: of a second electron gun structure, a so-called read-out gun of conventional construction, comprising a cathode 23 and an anode 24, and including additionally all the necessary focusing and control electrodes of conventional construction not shown herein in detail; and of a second sweep system for example, an electrostatic sweep system comprising two pairs of deflecting plates 25 and 26, conventional means (not shown) being also provided for applying to each of these plates suitable sweep voltages.

The base 27 on which are grouped the feed or supply pins of the reading system, comprises, among others, a pin 28 connected to the cathode 23, and to which is applied by way of terminal 29 a negative voltage V1 of the order of 1.5 to 2 kv. Since the anode 24 is connected to ground, a difference of positive potential equal to this voltage is established between the anode 24 and the cathode 23. The supplies of the other electrodes of the gun structure by way of other pins at the base 27 have not been shown since they are conventional and may utilize any voltage values necessary to that effect.

According to the present invention, the target 13 of which an enlarged cross sectional view is shown in FIG- URE 2, comprises not only a very thin metallic layer 30 of the order of 0.03 to 0.1 micron, of a metal such as aluminum, facing the writing gun structure, and an insulating layer 31 that is also very thin, approximately of the order of 0.5 micron, made of a dielectric such as zinc sulfide conferring to the target a high coefficient of multiplication, this insulating layer facing the read-out gun structure, but also a grid 32 (FIGURES 2 and 3), on the side of the read-out gun structure, disposed on the insulating face of the layer 31 by any known process such as the vaporization in vacuum. This grid 32 is made of a suitable metal, such as aluminum, and is realized with a sufficiently large transparency, at least 50% and with a suflicient number of meshes per mm at least 40, in order that the spot of the read-out gun structure covers several meshes. Since the potential of metallization 30 is fixed to that of ground by the intermediary of the resistance 33, the potential of the grid 32 is determined by the source 34 and is adjustable by means of the potentiometer 35. If one desires additionally to superimpose on this potential rapid variations, one may apply a control signal to the resistance 36 by way of capacitor 37, the source 34 being then uncoupled by means of capacitor 38.

Since the operation of the described analyser storage tube having induced conductivity is widely known, it suffices to recall that the application of an input signal at causes to inscribe on the insulating face 31 a potential relief from which one obtains an output signal at 19 after sweeping the target by the read-out beam. Consequently, the description herein is limited to the modification of the operation in relation to the improvement introduced by the present invention.

This modification may be explained in the following manner.

Since the grid 32 has a number of meshes per mm such that the spot of the read-out gum covers several meshes, this gun deposits positive charges between the meshes, and depending on the polarity of the grid 32, these charges may or may not flow-0H? by induced conductivity. If the grid 32 is at the potential of ground, that is at the potential of conductive face 30, a portion of the induced electrons is prevented from attaining the positive charges, and the more the grid 32 is negative with respect to this conductive face, the greater the number of induced electrons that are prevented from attaining the positive charges. This grid 32 therefore behaves as a modulating electrode of the current of secondary electrons on the inside of insulation.

By varying the coeflicient of multiplication of the grid, it is possible to obtain the absence of the output signal, therefore to erase all or part of the inscribed image in relief of charge on the target. One may also modify by the same means the amplitude of the output signal, and therefore may, for example, cause varying the contrast, correct the shading, etc.

It may be readily seen from the foregoing that the application of the grid on the target with induced conductivity in analyser storage tubes of the type described hereinabove permits interesting operational possibilities among which have been mentioned only a few as nonlimitative examples.

While I have shown and described one embodiment in accordance with the present invention, it is obvious that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person killed in the art, and I therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. A storage electron tube comprising:

target means including an insulating layer of a material providing induced conductivity properties, a metallic layer coating one face of said insulating layer, and a metal grid in contact with the opposite face of said insulating layer;

means including a source of a fast electron beam for bombarding said metallic layer with said fast electrons;

means for impressing input signal on said last-mentioned beam;

means including a source of a read-out electron beam for scanning said opposite face with said last-mentioned beam;

means for obtaining output signals responsive to said scanning;

and means for varying the electron multiplication factor of said target including means for varying the potential of said metal grid;

the size of a mesh of said metal grid being a fraction of the cross section of said reading beam.

2. A storage electron tube comprising:

target means including an insulating layer of a material providing induced conductivity properties, a metallic layer coating one face of said insulating layer, and a metal grid in contact with the opposite face of said insulating layer;

means including a source of a fast electron beam for bombarding said metallic layer with said fast electrons;

means for impressing input signal on said last-mentioned beam;

means including a source of a read-out electron beam for scanning said opposite face with said last-mentioned beam;

means for obtaining output signals responsive to said scanning;

and means for varying the electron multiplication factor of said target including means for varying the potential of said metal grid, and means for electrically controlling the potential variations of said' metal grid;

the size of a mesh of said metal grid of being a fraction of the cross section of said reading beam.

3. A storage electron tube comprising:

target means including an insulating layer of a material providing induced conductivity properties, a metallic layer coating one face of said insulating layer, and a metal grid in contact with the opposite face of said insulating layer;

means including a source of a fast electron beam for bombarding said metallic layer with said fast electrons;

means for impressing input signal on said last-mentioned beam;

means including a source of a read-out electron beam for scanning said opposite face with said last mentioned beam;

means for obtaining output signals responsive to said scanning;

and means for varying the electron multiplication factor of said target including means for varying the potential of said metal grid, and means for electrically controlling the potential variations of said metal grid;

the size of a mesh of said metal grid being a fraction of the cross section of said reading beam.

4. A storage electron tube comprising:

target means including an insulating layer of a material providing induced conductivity properties, a metallic layer on one face of said insulating layer, and a metal grid on the opposite face of saidinsulating layer;

means including a source of a fast electron beam for bombarding said metallic layer to inscribe an image thereon with fast electrons;

means including a source of a read-out electron beam for reading-out the image on said target;

and means enabling adjustment of the electron multiplication factor of said target by directly varying the potential of said grid;

the size of a mesh of said metal grid being a fraction of the cross section of said reading beam. 5. In a storage tube of the type having an inscription gun structure, a reading gun structure producing a read- 5 ing beam, and a target providing induced conductivity,

the improvement essentially consisting of means including a grid structure on said target for controlling the multiplication coefficient of said target by directly applying control voltages to said grid structure;

the size of a mesh of said grid structure being a fraction of the cross section of said reading beam.

6. In a storage tube of the type having an inscription gun structure, a reading gun structure producing a readr ing beam, and a target providing induced conductivity,

References Cited by the Examiner UNITED STATES PATENTS 2,587,830 3/1952 Freeman 315l0 2,728,872 12/1955 Smith 315-12 2,900,555 8/1959 Schneeberger 313-65 X OTHER REFERENCES Knoll et al.: Storage Tubes, John Wiley and Sons,

Inc,. New York, 1952, p. 15.

DAVID G. REDINBAUGH, Primary Examiner, 

1. A STORAGE ELECTRON TUBE COMPRISING: TARGET MEANS INCLUDING AN INSULATING LAYER OF A MATERIAL PROVIDING INDUCED CONDUCTIVITY PROPERTIES, A METALLIC LAYER COATING ONE FACE OF SAID INSULATING LAYER, AND A METALLIC GRID IN CONTACT WITH THE OPPOSITE FACE OF SAID INSULATING LAYER; MEANS INCLUDING A SOURCE OF A FIRST ELECTRON BEAM FOR BOMBARDING SAID METALLIC LAYER WITH SAID FAST ELECTRONS; MEANS FOR IMPRESSING INPUT SIGNAL ON SAID LAST-MENTIONED BEAM; MEANS INCLUDING A SOURCE OF A READ-OUT ELECTRON BEAM FOR SCANNING SAID OPPOSITE FACE WITH SAID LAST-MENTIONED BEAM; 